Phone or call systems employ various methods or protocols to notify system users when a triggering event arises, such as an emergency situation, in the area. General areas of triggering events might be a terrorist attack, a natural disaster, or an industrial accident. Examples could include release of a toxic substance into the atmosphere, radiation release from a nuclear facility, impending tidal wave, hurricane, or tornado, or a flash fire. Such triggering events would be occurrences in which people would need to be notified immediately or at least as soon as possible so that proper action can be taken.
Conventional wide-area alerting systems might automatically initiate alerting calls to thousands of users in the system, based on a pre-defined list of phone numbers. The system sequentially calls the numbers one at a time and processes each call depending on the outcome of the call. If a person answers, the system note that this number does not need to be called again. If an answering machine picks up or if there is no answer after a predetermined number of rings, the system notes this and will attempt the number again at a later time. This static type of alerting can take a very long time to complete, since only a limited number of calls can be made during any given time. In addition, the efficiency of such a system can be very low. For example, assume that calls to most of the numbers at the top of list are not answered by a live person, but that numbers at the bottom of the list do have live people by the phone. In this situation, the people associated with the bottom numbers needlessly have to wait while the system goes through many unanswered numbers.
Therefore, there is a need for a more efficient call alerting system that overcomes the disadvantages of conventional system discussed above.
Like element numbers in different figures represent the same or similar elements.